P-P with some muscle

[DougL]

I'm curious, and I'm being totally serious and not trying to be an A$$, am I just cheap? I make a good living but the wife only gives me so much allowance per month. 1K seems like a pretty serious investment to me for a DIY amp, especially something that doesn't seem to be too incredibly outlandish/esoteric; a basic P-P amp making 50-60 watts per channel with KT88/6550 tubes doesn't seem like it should break the bank. Is everyone else spending that kind of cash?

I think the $1k was parallel KT88. A PP EL84 can be done for $300 or so. I would think a single KT88 design would be between those figures.
One of your main issues is going to be weight. A 50W transformers should be heavy.
A power transformer to drive it should be heavy.
The case its in needs a heavy plate to hold the transformers.
Dyna made the Mark 3 mono so they could be carried my one person. Not because of any technical advantage.

Doug

 

[chrish]

thats the one George - a great thread that investigates a number of design options and has come up with a good working design. I understand that Chris has all the parts in hand now - perhaps he can give a comment on the (present) cost...

After all of the support coming up with a schematic that should work, I feel bad that I have not started building. Unfortunately I have had some personal issues that have lead me to move house. I don't have a proper workshop, so the chassis work is going to be difficult. I have some real nice aluminium chassis for the mono-bocks, but the top plate is 3-4mm thick, which means I cant use chassis punches I have and will have to drill or router. Will have to sort out a solution...

As for cost - not cheap. The two Tamura output transformers were about $300 Australian dollars each. The two Hammond 300BX power transformers are now about $150 USD each. The chassis were a couple of hundred, assorted electronics - couple hundred, tubes - couple hundred. Hate to add it up, but I have collected the parts over a year or so.

I do aim to start doing something soon...

Cheers,
Chris

 

[Steven-H]

I've got a pair of those OPT's stashed away for a PPP monoblock project,Just waiting for George's Universal PP driver boards.

Hehe...and I have two whole amps !

 

[Tubelab_com]

When running AB2, is there a problem with transformer saturation? That is to say is it necessary to use a gap core to avoid saturation since one side will be completely in cut-off while the opposite side is driving the core?

No, By definition one side of a push pair will be cutoff any time you leave pure class A. This happens in AB1, AB2, or B. The only difference between class AB1 and AB2 is the presense of grid current in the output tubes. If the driver is designed to supply the grid current without ANY distortion class A2 or AB2 can provide good HiFi sound. This is not a trivial task and the ability of the driver to source grid current, and the ability of the output tubes to stand grid current determines how deep you can go into A2 or AB2 without distortion. Driver transformers and cathode followers are the traditional method and these will allow for shallow AB2 and go a long way toward elimination of overload recovery artifacts. Improvement over the traditional methods involves mosfets (simple and effective) or "augmented cathode follower" driver circuits (very complicated, but very effective).

I'm curious, and I'm being totally serious and not trying to be an A$$, am I just cheap?

I will guarantee you that I have never spent $1K on an amplifier, and I doubt that I ever will. On the other hand several builders spent more than that on their Simple SE's, but mine cost me under $300. I will carefully shop for parts and grab what I can when I see a deal (hence the monster OPT's) saving some big bucks along the way. I can add up the total cost when I am done and I will be surprised if it is over $500. It sounds like Chrish has nearly $1K in the transformers, so a $1K amp is a real possibility.

Taking a quick look around the web for new quality parts yields this:

Edcor 100 watt OPT's $92 each $184
Antek toroidal power transformer $50
EH KT88's $64 per pair $130
Sovtek 6SN7's $10 each $40
PC boards and small components $200
Chassis $100

Total $704


I am assuming solid state rectifiers and I am probably forgetting something, so $1K is possible with all new parts purchased from the common sources. Remember that the OPT is the most important component in any tube amp and I am sure that the $92 Edcors will whip up on amything that comes stock in a Chinese amp. I am also assuming the use of my Octal Driver circuit, which is a bit more complicated than the 12AX7 - 12AU7 circuit found in many low cost amps.